The present invention is generally related to microscope systems used to observe and/or direct laser eye surgery. In particular, the present invention provides devices, systems, and methods for structurally supporting the optical elements of a microscope relative to the optical train of the laser delivery system. The present invention is particularly useful for optically observing laser surgical procedures such as photorefractive keratectomy (PRK), phototherapeutic keratectomy (PTK), laser assisted in situ keratomileusis (LASIK), or the like.
Ophthalmic laser surgery and other ophthalmic procedures are often performed by a laser after optically aligning the laser with the eye using a microscope. While it may be possible to make use of lasers having other wavelengths, known laser eye surgery procedures generally include an ultra-violet or modified frequency infrared laser to remove a microscopic layer of stromal tissue from the eye""s cornea to alter its refractive power. In one application, the laser removes a selected portion of this corneal tissue in order to correct refractive errors of the eyes. Laser ablation results in photodecomposition of the corneal tissue, but generally does not cause significant thermal damage to adjacent and underlying tissues of the eye. The irradiated molecules are broken into smaller volatile fragments photochemically, directly breaking the intermolecular bonds. The microscope is often used to observe the treatment during and/or after the ablation, as well as to align the ablation with the eye.
Laser ablation procedures can remove the targeted stroma of the cornea to change the cornea""s contour for varying purposes, such as for correcting myopia, hyperopia, astigmatism, and the like. While a variety of approaches and systems have been described for controlling the distribution of tissue ablation across the cornea, including masks, fixed and movable apertures, controlled scanning systems, eye movement tracking mechanisms, and the like, most laser eye systems include a microscope to aid the surgeon in aligning the patient""s cornea with the laser system, and to allow the surgeon to optically monitor or verify that the targeted portion of the stroma is removed as intended.
Known laser eye surgery systems have generally included fairly standard microscope structures. The focus and field of view of a conventional microscope is often controlled by shifting the specimen to be viewed relative to the microscope structure. To target the field of view of microscopes used for laser eye surgery upon the patient""s eye and allow observation of the laser beam delivery, these microscopes are instead often shifted in three dimensions relative to the support structure of the laser beam delivery system. Both positioning and stability of the microscope are tightly controlled, since any displacement of the microscope structure from proper alignment with the laser delivery location is magnified by the magnification of the microscope.
While these known laser eye surgery systems are quite effective, the cost and complexity of the microscope positioning and support structure are significant disadvantages. To provide adequate positioning and stability of the microscope relative to the laser delivery optical train, known laser eye surgery systems typically include a microscope adjustment structure having parts machined to tight tolerances. This adjustment structure often accommodates travel of the microscope in X, Y, and Z directions with a high degree of accuracy. These microscope adjustment mechanisms add significantly to the overall costs of the laser eye surgery system.
In light of the above, it would be desirable to provide improved laser eye surgery systems, devices, and methods. It would be particularly desirable to provide enhanced techniques for structurally supporting the microscope relative to the other components of the laser system. It would further be desirable if these improvements could be provided with less complexity, greater reliability, and a lower cost than known laser surgery/microscope support systems.
The present invention provides improved structures, systems, and methods for supporting the optical elements of a microscope relative to the optical train of a laser eye surgery system. The present invention generally takes advantage of a surprising characteristic of many microscopes: the field of view of the microscope can be substantially fully determined by the position of the objective lens. As a result, the field of view of the microscope can be fixed by accurately positioning just a portion of the many optical components of the microscope. In other words, the laser delivery optics and the microscope can be aligned with a target location of the patient""s eye by accurately aligning just the objective lens with the delivery optics. By structurally separating the objective lens from the other optical components of the microscope, and by maintaining accurate alignment between the objective lens and the laser delivery optics with a simple, tight-tolerance support structure, the remaining optical components of the microscope can be allowed to xe2x80x9cfloatxe2x80x9d relative to the objective lens with a looser tolerance without degrading the operator""s ability to align, observe, and optically direct a procedure, particularly when using a microscope having a Galilean magnification changer.
In a first aspect, the present invention provides a laser eye surgery system for resculpting a cornea of a patient. The system comprises a laser to produce a laser beam. Laser delivery optics are optically coupled to the laser so as to direct the laser beam toward the cornea of the patient. The laser directed by the laser delivery optics will generally alter refraction of the cornea. An optics support structure supports at least a portion of the delivery optics.
The laser eye surgery system further includes a microscope having an eyepiece, an objective lens, and a microscope body. The microscope body is attached to the optics support structure, and will directly support the eyepiece. Unconventionally, the laser optics support structure directly holds the objective lens in alignment with at least a portion of the delivery optics.
By supporting the objective lens and laser delivery optics with a common structural support system, the present invention can ensure alignment between the entire microscope and the treatment site. Advantageously, an off-the-shelf microscope can be modified for use in the present invention by removing its objective lens and mounting the microscope body and eyepiece on a mounting pad of the optic support structure. Even though the resulting positioning tolerance of the eyepiece of the microscope may be significantly looser than the positioning tolerance of the objective lens relative to the delivery optics, alignment is maintained between the field of view and treatment site. The laser beam will often be substantially coaxial with the objective lens, the objective lens often being disposed between the eyepiece of the microscope and a partially reflective mirror or other beam splitting structure. The off-the-shelf microscope will preferably comprise a binocular microscope having a Galilean magnification changer.
The optics support structure will generally restrain the objective lens of a microscope in fixed lateral alignment with a treatment axis of the laser beam. In production models, the objective lens will also be axially affixed relative to the treatment axis. Alternatively, particularly in pre-production development models of the present laser system, the axial position of the objective lens may be adjustable to determine the proper alignment between the field of view of the microscope and the laser delivery optics. Once this axial alignment has been determined, a variable axial positioner may be removed and replaced with a fixed spacer.
In another aspect, the present invention provides a method for fabricating a laser eye surgery system. The method comprises providing a microscope having an eyepiece supported relative to a mounting surface by a microscope body. An objective lens of the microscope, together with laser delivery optics, are mounted on a delivery optics support structure so that the optics support structure maintains alignment between the delivery optics and the objective lens with a first tolerance. The optics support structure includes a mounting pad, and the microscope body is attached to that mounting pad so as to align the eyepiece with the objective lens. The eyepiece is aligned with a second tolerance which is looser than the first tolerance.
Advantageously, the lateral alignment of the objective lens and a target axis of the delivery optics may be fixedly restrained by the optics support structure. An axial position of the objective lens may initially be determined using an adjustable positioner of the optic support structure. Once this axial position is determined, the adjustable positioner can be replaced with a fixed spacer to immovably restrain an objective lens at the determined axial position. This allows the field of view of the microscope to be permanently set at the desired position, and avoids having to resort to a complex, tight-tolerance, and expensive adjustment system for translating the microscope relative to the delivery optics in three dimensions. Fixing of the objective lens (and thereby the field of view of the microscope) also increases the efficiency of the system by eliminating the previously required steps of aligning the microscope with the targeted corneal tissues. Instead, the field of view of the microscope remains aligned with the treatment axis of the laser delivery optics when the cornea is positioned, generally by moving the entire patient on a moveable operating table.